so it's a commonly used technology. >> would the fbi and law enforcement be using this kind of technology throughout the week at night as they searched? i guess only the search really began thursday evening after they began looking for dzhokhar. but were they probably out there deployed looking with thermal image to go see if there were any unusual heat signatures? >> yeah, i noticed on the night of the shooting of the police officer at m.i.t. that you could see helicopters hovering in the air at that time. just depends. the human body is going to be warmer especially in the cooler night air. and the city lights down there, they might use equipment which takes the ambient light that's already there from street lights and traffic lights and amplifies it a little bit. so there are different technologies depending on the amount of available light at the scene and time of day that it is. >> and brash bra star, barbara starr, if it you're there, this is the kind of technology that military uses all the time. >> absolutely. it didn't get to the point of lee that himity at the end game. but this